Visual testing system for electromagnetic sound reproducers



Dec. 7 1926.

- c. E. BRIGHAM VISUAL TESTING SYSTEM FOR ELECTROMAGNETIC SOUND REPRODUCERS Filed June 16, 1924 2 SheetsSheet 1 FIG:

CfC/L E. BZ/G-HAM INVENTOR.

A TT ORNE Y.

Dec. 7 {1926.

c. E. BRIGHAM v VISUAL TESTING SYSTEM FOR ELECTROMAGNETIC SOUND REPRODUCERS Filed June 16. 1 924 2 Sheets-Sheet 2 kmwk. 2o kwiwvmm w wt CECIL E. BZ/GHAM INVENTOR.

A TTORNEY,

Patented Dec. 7, 1926.

UNITED STATES v 1,6,398 PATENT OFFICE.

CEC IL E. BRIGHAM, OF EAST ORANGE, NEW JERSEY, ASSIGNOR, BY MESNE ASSIGN- MENTS, TO BRANDES LABORATORIES INC., OF NEWARK; NEW JERSEY, A CORPORA- TION OF NEW JERSEY.

VISUAL TESTING SYSTEM FOR ELECTROMAGNETIC SOUND REIRO DUCERS.

Application filed June 16,

My invention relates broadly to testing systems and more particularly to a visual testing system for determining the properties of acoustic instruments.

One of the objects of my invention is to provide an electrical system for rapidly testing such acoustic instruments as electromagnetic sound reproducers, loud speakers or telephone receivers on a quantity production basis wherein devices falling within given limits, designated by the testing apparatus, will have such properties that they are acceptable for use, while devices falling outside of the particular limits may be rejected.

Another object of my invention is to provide an electrical testing system for telephone receivers wherein numbers of receivers may be tested in succession by an operator who is required to do nothing more than to place each receiver to be tested upon a test board on the apparatus and observe the deflection of a meter to determine the electrical properties of the receiver on test.

Still another object of my invention is to provide a visual testing system for telephone receivers wherein a plurality of electron tube circuits are employed, each having input and output circuits with a meter arranged at the output circuit of the last tube and a telephone receiver to be tested adapted to be connected in the input circuit of the first tube whereby sound vibrations impressed upon the telephone receiver cause variable readings upon the meter whereby the electrical properties of the receiver on testmay be determined.

A further object of my invention is to provide a visual testing system whereby telephone receivers may be rapidly examined as to volume and sensitivity by comparing the operation of a telephone receiver whose properties are to be determined with the operation of a standard telephone receiver of selected properties whereby visual readings of the relative properties of the telephone receivers may be obtained.

My invention contemplates the testing of telephone receivers wherein an audio frequency oscillator is employed for impressing audio'frequency energy upon either a standard telephone receiver or a telephone receiver w ose properties are to be determined,

1924. Serial No. 720,417.

whereby the telephone receiver whose properties are to be determined may be alternately a sound reproducer or a receiver of sound waves.

The comparative tests for volume and sensitivity are computed upon a basis of the force which is required to move a sound reproducing diaphragm. From a study of the properties of electromagnetic sound reproducers the value of current necessary in the windings of the electromagnetic operating mechanism to move the diaphragm at an amplitude to produce a certain volume of sound is readily determined. On the other hand, the volume of sound necessary to move a diaphragm in the field of the magnet coils within the sound reproducer to induce therein a certain value of current may also be readily determined. I therefore provide an electromagnetic device which is termed a standard and which serves as a generator of sound when the electromagnetic device on test is to be passed through a sensitivity test. That is, the standard emanates sound which impinges against the diaphragm of the electromagnetic device on test in order to determine the sensitivity of the device on test. When however the device on test is to be studied from the viewpoint of volume reproduction, the testing device itself is used as a sound generator for directing sound vibrations against the standard.

I provide an electron tube amplification circult consisting of a plurality of electron tubes, each having grid, filament and plate electrodes. In the input circuit across the grid and filament electrodes of the first tube either the windings of the standard telephone receiver or the telephone receiver whose properties are to be determined may be connected. The last tube of the amplification system is connected independently of the other tubes and includes a meter in its output circuit. This meter is provided with a reverse reading scale whereby decreases of energy in the plate circuit are readily observed. When sound vibrations are impressed upon a telephone receiver connected in the input circuit of the amplification system the magnetic membrane or diaphragm is caused to vibrate, varying the flux from the horseshoe magnet in the receiver, inducing varying currents in the telephone receiver windings and causing a.

' of the last tube of the system. By alternately connecting the standard telephone receiver and the telephone receiver whose properties are to be determined in the input circuit of the amplification system the receiver on test may be examined both as to volume and sensitivity.

My invention Willbe more fully understood from the following specification by reference to the accompanying drawings, 1n

which:

Figure 1 is a front view of the visual testing apparatus as assembled; Fig. 2 is a side elevation of the complete visual testing apparatus; Fig. 3 is a'theoretical dia-' gram illustrating one of the acoustic principles employed in my invention; Fig. 4 is a diagrammatic circuit arrangement showing the visual testing system as herein described; and Fi 5 shows the reverse reading scale with w 'ich the meter in the output circuit of the apparatus is equipped.

Heretofore in the art in the manufacture and production of telephone receivers on a quantity production basis it has been customary .to merely test the telephone receivers by ear. That is to say, the completed telephone receivers would be passed through an inspection room where a number of operators would connect the individual tele-' phone receivers in an electrical circuit and listen" for a brief interval to determine whet-her the receiver would properly respond to a signal. This method has many disadvantages important among which is the human equation and the possibility of improper inspection by lack of care 1n examining the receiver on test. The testing of telephone receivers in this manner is largely dependent upon the acuteness of the hearing ability of the operator which may vary with different operators to such' an extent that telephone receivers rejected by one operator might actually be passed by a differ ent operator, resulting in a non-uniform production. The'uniformity in the electrical properties of telephone receivers is of the utmost importance where a pair of such tele-' phone receivers are employed in the reception of radio broadcast signals. In order to insure that telephone receivers have properly matched tone I have provided the visual testingsystem herein described which renders the testing of telephone receivers to a large extent automatic insurin a uniformity in product with ultimate high eficiency 'in operation of the headset equipped with ,matx'hed tone telephone receivers.

30 and 33.

Referring more particularly to the drawing's, reference character 1 designates the amplifier unit of the visual testing apparatus. The cabinet containing the visual testing apparatus is represented at 2 which serv'esas a support for the amplifier unit 1. A compartment 3 is provided in one side of cabinet 2 in which maybe placed batteries for the electron tube circuits or other. power supply equipment.

An anti-capacity switch 4 is providedon the panel of the visual testing apparatus to enable the operator to alternately test a telephone receiver placed upon test board unit 5 either as to volume or sensitivity. The

direct current 'microammeter 6 is mounted on the visual testing apparatus as shown in a position where its scale may be readily observed by the operator' Fig. 4 shows the wiring diagram for the equipment. An audio frequency master oscillator is provided including electron tube 8 having coupled input and output circuits 9 and 10. The frequency of the oscillator is determined by capacities 11, 12 and 13 which may be independently connected in the oscillator circuit. The amplitude of the oscillations produced by the master oscillator may be increased by electron tube amplifier 14 having its input circuitcoupled with the output circuit of the master oscillator through inductancesand amplifier is supplied from a common source 19. The plate potential for the tubes maybe derived from source B; It will be understood that the master oscillator as described may serve as a supply for a number of visual testing equipments in charge of different operators in the test room. The anticapacity switch 4 provided on the panel of a the testing apparatus consists of a rocking cam which when moved to one direction causes contacts 21 to close an electrical circuit through contacts 42, while contacts 22 close an electrical circuit through contacts 41.

When the rocking cam is moved in the 0pposite direction contacts 21 close an electrical circuit through contacts 40, while contacts 22 close an electrical circuit through contacts 43. A standard telephone receiver of selectedpropertiesis provided on the equipment as represented by reference character 44 and is permanently connected with contacts 42 and 43. The telephone receiver whose properties are to be determined is represented at 45, a sliding contact being completed between the terminals onthe telephone receiver and brush contacts which are permanently connected with terminals 40 and 41 of the anti-capacity switch 4. The amplification system 1 consists of electron tubes 24, 26,

lau-

Resistance 25 is connected across .coupled with the output circuit of the preceding tube through variable capacity 34 and resistance 35. The tube 33 is independent of the preceding tubes in that it has a separate filament control 36 independent of the filament control 29 of the A circuit from battery 37 of tubes 24, 26, and 30. B battery 38 and 39 is employed for tubes 24, 26 and while a tap at batterv 38 is taken for the B otential for tube 33. This voltage is rat er critical and should be maintained to obtain the zero reading on the direct current microammeter 6. Normally this voltage is approximately twenty-two and one-half volts.

Referring to Figure 3, the standard telephone receiver 44 is represented as connected through contacts 42 with terminals 21 of the audio frequency oscillator in such manner that sound waves 48 are set up; These sound waves are directed against the diaphragm 47 of the telephone receiver 45 whose properties are to be determined. The magnet windings 46 of this telephone receiver are connected through contacts 41 with terminals 22 of the input circuit of the amplification system 1. The magnetic membrane or diaphra m 47 is caused to vibrate as represented w ereby the flux is varied from the horseshoe magnet in the telephone receiver. Thisinduces varying currents in the magnet winding 46 causing a variable potential in the input circuit of tube 24. Tubesv 26, 30 and 33 'operate to increase the amplitude of this variable potential impressing the increased energy 'upon the the master oscillator are energized.

microammeter 6. The microammeter 6 is provided with reverse reading scale 49 illustrated'in Fig. 5, the indicator 51 moving counter-clockwise as represented b arrow 50. In the'operation of thevisua testing system the audio frequency oscillator is connected with the visual tezting apparatus with the positive terminal 16 ofthe oscillator connected to the positive terminal 21 of i the anti-capacity switch 4. The filaments of the oscillator and amplification tubes for en the cam device of the anti-capacity switch 4 is rocked to" the right, terminals 21 make connections with contacts 42 whereby the standard telephone receiver 44 acts as a generator of'sound vibrations'for the sensitiv ity test. The frequency of this sound is controlled by thesw-itch which connects condencers 11,12 and 13 or combinations therein the audio frequency oscillator circuit.

stat 36 is moved slowly until the reading of indicator51. on scale 49 reaches zero. The variable condenser 34- or sensitivity control is now placed at maximum capacityand the visual testing apparatus is ready to op erate. The receiver whose electrical properties are to be determined is placed on the test board 5 with its terminals making connection with spring clips 52 which connect with contacts "40 and 41 of anti-capacity switch 4. On a"sensitivity test wherethe standard telephone receiver 44 acts as the generator of sound vibrations the telephone receiver 45 to be tested is automatically connected to contacts 41 with terminals 22 to the input circuit of the amplification system '1. The diaphragm of the receiver on test is vibrated by the sound vibrations emanatin from standard receiver 44 and the grid e ectrode of the last tube 33 is energized in such manner that the current in the plate circuit and through microammeter 6 iminishing proportionally Indicator 51 therefore tends to swing counter-clockwise over scale 49 giving the optical illusion of increase in scale reading by reason of the reverse scale arrangement. That is, to say, the sensitivity test is one in which the amount of reduction in plate current in tube 33 is observed.

I- have determined that limits for acceptable receivers with regard -to sensitivity should be approximately within and 160 scale readings, that is, the telephone receiver on test should give a reading between 100 and 160 in order that it shall be acceptable. I have found that telephone receivers which are rejected by reason of readings below 100 generally have such defects as:

(8 Weak magnets;

Lacquer on diaphragm. 9 Low poles.

Non-magnetic diaphragm. Te ephone receivers on test which give readings above 160 generally have the fol lowing defects:

a High poles. 7

6 Iron grindings on poles. 0) Loose caps. d) Bent dia hragm.

quick chec is available in'the produc-' 2 tion of telephone receivers by the methods herein described. Volume tests are made by rocking the cam switch 4 to the left therebyconnecting terminals 21 of the audio frequency oscillator with contacts 40 whereby 39 the receiver on test serves as a generator of sound vibrations which are picked up by standard receiver 44 connected through contacts 43 with terminals 22 and the input circuit of amplification system 1. The deflections of microammeter 6 will now show the volume characteristics of the telephone receiver on test. I have found that in general a difference in scale readings greater than 30 between sensitivity and volume requires that the receiver on test should be held for examination as a rejection.

The visual testing system and apparatus of my invention may be employed in determining the characteristics of loud speakersv what I claim and desire to secure by Letters Patent of the United States is as follows:

1. A visual system for testing telephone receivers comprising in combination a generator of oscillations, a pair of telephone receivers, one of saidtelephone receivers consisting of a standard and the other of said receivers consisting of the unit on test,

said unit being acoustically coupled to said aforementioned telephone receiver, means for connecting said oscillator alternately to either of said receivers, amplification means, a meter connected therewith and means for connecting the receiver not connected with said oscillator with said amplification means.

2. A visual system for testing telephone receivers comprising in combination means for generating a sustained tone frequency, a pairfi telephone receivers one comprising a standard and the other comprising a receiver whose characteristics are to be determined, said last mentioned receiver being acoustically coupled with said standard, means for impressin said sustained tone frequency on either 0 said receivers, a measuring circuit including either one or the other of said receivers and means for observing the current values in said circuit. p

3. A visual system for testing telephone receivers comprising in combination a standard telephone receiver, a receiver .whose characteristics are to be deterl'fiined laid receivers being acoustically-coupled, a fi' generator of sustained tone frequencies,

means for impressing said frequencies on either one or the other of said receivers whereby either one or, the other of said receivers operates as a sound producer or receiver impressing said frequencies on either one or the other of said receivers and means for observing the current in said circuit and testing said receiver whose characteristies are to be determined both as t sensitivity and volume.

4. A visual system for testing telephone receivers comprising in combination an electromagnetic sound producing means, a telephone receiver whose characteristics are to be determined adapted to be acoustically connected with said sound producing. means operating to collect the sounds thus produced, a circuit-connected with said last mentioned telephone receiver and means in said circuit whereby current therein decreases When said electromagnetic sound producing means is operated.

5. A visual system for testing electromagnetic sound reproducers comprising in combination an electron tube oscillator arranged to generate sustained oscillations each of selected constant tone frequencies, means for increasing the amplitude of the tone frequencies thus produced, a pair of electromagnetic sound reproducers one of which is a standard and the other of which is a reproducer to be tested, each arranged to transmit or receive sound waves in either of two directions, an electron tube amplifier having input and output circuits, 'a meter connected in the output circuit of said electron tube amplifier, means for alternately connecting either of said electromagnetic sound reproducers with said oscillator or with the input circuit of said amplifier whereby said meter operates to indicate sensitivity of said reproducer to be tested when said standard reproducer is connected with said oscillator and to indicate volume character-' istics of said reproducer to be tested when said last named reproducer is connected with said oscillator.

6. A visual system for testing electro magnetic sound reproducers comprising in combination a standard electromagnetic sound reproducer, an electromagnetic sound reproducer whose characteristics are to be determined, means for impressing oscillations of a predetermined constant tone frequency on either of said reproducers whereby the other reproducer operates as a sound collector actuated by sound waves produced by the reproducer connected -with said means, a pluralityof electron tubes having grid filament and plate electrodes, input and output circuits, a meter connected in the output circuit of the last tube of the series, -means for impressing .a negative charge on the grid electrode of said last named tube whereby current in said plate circuit decreases as said oscillations are impressed on either of said electromagnetic sound reproducers.

7. A visual system for testing electromagnetic sound reproducing devices comprising in combination an electron tube amplifier circuit, a meter actuated by said circuit, and a pair of acoustically coupled electromagnetic devices which may be alternately connected with the amplification 10 circuit by a switching mechanism, one of the devices being an instrument whose electrical properties are to be determined and which may be used alternately as a sound generator or receiver for determination of 15 sensitivity and volume of the instrument on test.

CECIL E. BRIGHAM. 

